AceD wrote:The timeline is correct, i posted this on another forum to explain so i'll just paste it here

Railgun season 1 covered volumes 1,2 and 3. Which is the level upper arc (+2 filler arcs)Railgun S is starting on volume 4, it will probably run through 5 and 6. Which will be the full sisters arc from the Railgun manga.

Index season 1 covers the first 6 volumes, volume 3 is the sister arc from the Index novel.

Railgun season 1 starts before Index season 1. Railgun S1 ends before volume 1 of Index ends. Basically, Railgun S1 ends around episode5/6 (whenever it was Touma was unconscious for a few days after being whipped by Kanzaki)

Sooooooo Railgun S is taking place between episodes 9 and 10 of Index S1. Episode 10 is when the sisters arc (Index POV) begins. Between episode 9 and 10(or volumes 2 and 3 if you like) there is a 2 week gap. This 2 week gap is Railgun S.

Index anime begining = July 19thRailgun = July 16thSo yeah Railgun starts a bit before Index, but not that much actually. Both anime (Index S1 and Railgun) take place kinda at the same time.

I actually thought it would be easier to understand explaining how things fit together volume & episode wise, rather than time wise. I guess anybody who wants to know the exact timeline of events can just go here though.